1. Department of Energy Saving and Air Protection, Central Mining Institute, Plac Gwarkow 1, 40-166 Katowice, Poland
2. Department of Economics, Finance, Regional and International Research, Opole University of Technology, Luboszycka 7, 45-036 Opole, Poland
3. Central Mining Institute, Plac Gwarkow 1, 40-166 Katowice, Poland
4. Spolka Restrukturyzacji Kopaln S.A., Strzelców Bytomskich 207, 41-914 Bytom, Poland